The present invention relates to mobile communications systems. More particularly, the present invention relates to the selection of one or more adaptive or sector antennas in a mobile communications system that employs multiple antennas per base station.
HIPERLAN/2 is a short-range, high data rate, cellular, broadband radio access network, which is mainly intended for indoor operations such as offices, conference halls, exhibitions, airports and home environments. Some outdoor scenarios are also being considered (e.g., campus areas and concentrated urban areas). The frequency spectrum to be used for H/2 is currently unlicensed. Thus, several xe2x80x9coperatorsxe2x80x9d may use the same frequency spectrum simultaneously. Furthermore, the available frequency spectrum for this system is very limited; consequently, it has been questioned whether it is possible to deploy such a cellular network.
Adaptive and/or sector antennas can be utilized to improve the capacity in such networks. With these antennas, a base station (BS) can restrict its transmission to a more definitive area or sector in which a given mobile terminal (MT) is located. Thus, radiated power into nearby areas or sectors, and interference to surrounding cells can be drastically reduced, as illustrated in FIG. 1.
Generally, in systems that employ these techniques, the uplink signaling is transmitted before the downlink signaling. The BS can then use the uplink signal to measure the relative direction of the MT. Upon determining the direction of the MT, the BS selects one of several antennas for communicating with the MT. However, this general procedure is often unacceptable, particularly when only downlink traffic is present, as the BS has no uplink signal with which to measure the relative direction of the MT. Accordingly, it would be more advantageous if the MT initiated and selected the BS antenna, rather than the BS, since the MT always knows its location. Presently, though, there exists no such protocol or technique.
The present invention involves a technique that improves the capacity in cellular, broadband radio access networks that employ multiple antenna base stations (BSs), where each cell is divided into sectors and each base station antenna is associated with a corresponding sector. Unlike conventional techniques, mobile terminals (MTs) in the present invention are employed to identify the most appropriate BS antenna from amongst multiple BS antennas. By using the MTs to identify the most appropriate BS antenna, rather than the BS, the BS antenna selection process is accomplished more efficiently and effectively, even when there is no significant uplink transmission between a given MT and the BS.
Accordingly, it is an objective of the present invention to improve the BS antenna selection process in a cellular, broadband radio access network that employs multiple antennas per BS.
It is also an objective of the present invention to improve the signal quality of the communication links between the MTs and the corresponding BS which employs multiple antennas.
It is still another objective of the present invention to reduce or minimize radiated energy and interference levels in other sectors or other cells proximally located to the sector in which a given MT is presently operating.
In accordance with one aspect of the present invention, the above-identified and other objectives are achieved through a method and a corresponding apparatus for selecting one of several base station antennas, wherein each of the base station antennas covers a corresponding sector of a cell associated with the base station. The method and corresponding apparatus involve transmitting a number of sector messages from the base station, where each sector message is associated with a corresponding sector of the cell. At a mobile terminal, the sector messages transmitted by the base station are received. The mobile terminal then determines a signal quality associated with each of the received sector messages, and based on this determination, the mobile terminal selects one of the antennas. The mobile terminal then transmits an antenna selection request message to the base station.